Contract No. 68-01-3163, Task No. 4
Final Report No. IITRI-C6333C04-3
TECHNOLOGICAL PROBLEMS OF BURNING
LOW-SULFUR WESTERN COAL
Engineering Investigating Section
Air Enforcement Branch
Enforcement Division
U.S. Environmental Protection Agency
Region V
Attention: Steve Rothblatt
Project Officer
Prepared by
Linda L. Huff
With contributions by
Willard R. Haas
IIT Research Institute
10 West 35th Street
Chicago, Illinois
December 31, 1975
U.S. Environmental Protection Agency
Region 5, Library (Pt-12J)
77 West Jackson Boulevard, 12th Floor
Chicago, JL 60604-3590
-------
FOREWORD
In Task No. 4 of EPA Contract No. 68-01-3163, we have
examined some of the technological problems of burning low-
sulfur coals in boilers. This report presents the data
collected and evaluated with regard to this problem.
Respectfully submitted,
I IT RESEARCH INSTITUTE
Linda L. Huff
Associate Economist-Engineer
Chemical Engineering Research
Approved by
%L
/John D. Stockham
(^/Scientific Advisor
Manager
Fine Particles Research
LLH/nb
IIT RESEARCH INSTITUTE
11 IITRI-C6333C04-3
-------
TABLE OF CONTENTS
Page
1. INTRODUCTION 1
2. EXECUTIVE SUMMARY 1
3. COAL TYPES AND THEIR IMPORTANT ATTRIBUTES 6
3.1 Coal Types 6
3.2 Attributes of Coal Important to Boiler Design . 11
4. GENERAL DESCRIPTION OF BOILER TYPES 11
5. CYCLONE BOILER 15
5.1 Cyclone Boiler Operation 15
5.2 Usage of Low-Sulfur Western Coals in Cyclone
Boilers 19
5.2.1 Boiler Design for Western Coals 19
5.2.2 Fuel Conversion Experience 20
5.3 Cost of Utilizing Western Coals 25
5.3.1 Boiler Replacement 25
5.3.2 Crushing Equipment 26
5.3.3 Conclusions on Conversion 26
6. TRAVELING GRATE STOKER 26
6.1 Traveling Grate Operation 27
6.2 Usage of Western Coals in Traveling Grate
Stokers 30
7. UNDERFEED STOKER 31
7.1 Underfeed Stoker Operation 33
7.2 Usage of Low-Sulfur Western Coals 33
8. SPREADER STOKERS 33
8.1 Spreader Stoker Operation 35
8.2 Usage of Low-Sulfur Western Coals in Spreader
Stokers 38
8.2.1 Stoker Design for Western Coals 38
8.2.2 Cost of Utilizing Western Coals 39
NT RESEARCH INSTITUTE
iii HTRI-C6333C04-3
-------
LIST OF TABLES
Table Page
1 Technological Problems of Boiler Operation. . . 3
2 Estimated Sulfur Content Distribution by Coal
Type 7
3 Comparison of Coal Characteristics 8
4 Range of Coal Characteristics 10
5 . Definition of Coal Characteristics 12
6 Coal Characteristics Affecting Boiler Design. . 13
7 Categorization of Boilers 14
8 Black Hills Power and Light Company Tests --
Typical Analyses 22
9 Characterization of Three Coals 23
10 Types of Pulverizing Mills for Various
Materials , . 43
11 Projected Coal Production from Federal Surface
Coal Mines for Steam Electric Plant Fuels for
1980-1981 50
12 Annual Coal Production (1969-1972) with
Estimates for 1973, 1975, 1980, and 1985. ... 51
13 Commonwealth Edison Coal Fired Generating
Stations 52
I IT RESEARCH INSTITUTE
v IITRI-C6333C04-3
-------
LIST OF FIGURES
Figure Page
1 Cyclone Furnace Operation 16
2 Cyclone Boiler System Design 18
3 Chain Grate Stoker Configuration 28
4 Simplified Fuel Bed Diagram 29
5 Stoker Design Criteria 32
6 Underfeed Stoker 34
7 Spreader Stoker Design 36
8 Pulverized Coal System 41
9 Firing Configurations of Pulverized Coal
Furnace 44
10 Mill Capacity Versus Fineness and Grindability. 45
\n RESEARCH INSTITUTE
vi IITRI-C6333C04-3
-------
TABLE OF CONTENTS (cont.)
Page
9. PULVERIZED COAL FURNACES 40
9.1 Pulverized Furnace Operation 40
9.2 Usage of Low-Sulfur Western Coals in Pulverized
Coal Units 46
9.2.1 Pulverized Coal Boiler Design 46
9.2.2 Conversion Costs of Pulverized Coal
Boiler for Western Coals 48
10. WESTERN COAL AVAILABILITY 48
REFERENCES 54
III RESEARCH INSTITUTE
iv IITRI-C6333C04-3
-------
TECHNOLOGICAL PROBLEMS OF BURNING LOW-SULFUR WESTERN COAL
1. INTRODUCTION
The burning of low-sulfur western coals in boilers designed
for bituminous fuels can result in operational problems.
Resolution of these problems requires modification of the
existing systems. In examining five boiler types, cyclone,
pulverized coal, spreader stoker, cross-feed, and under-feed
boilers, the necessary conversion factors were identified. The
costs associated with low-sulfur western coal utilization were
estimated where sufficient information was available.
To understand the significance of operational problems
in burning western coals, a background on coal characteristics
and boiler design is presented. This information serves as a
basis for discussion of the experiences in industrial and
power-generating usage of western coals.
2. EXECUTIVE SUMMARY
Technological problems of boiler operation do occur when
western coals are burned in those boilers designed to handle
midwestern or other types of coal. These problems have been
identified for the following five boiler types:
1. Cross-feed stoker
2. Under-feed stoker
3. Spreader stoker
4. Pulverized coal boiler
5. Cyclone boiler
These five boiler categories represent a wide range of
boiler sizes and types. Under-feed boilers, which usually have
capacities up to 20,000 pounds of steam per hour, are used
primarily in small industrial applications. Cross-feed and
spreader stokers are utilized in large and small industrial
applications with boiler capacities up to 400,000 pounds of
NT RESEARCH INSTITUTE
1 IITRI-C6333C04-3
-------
steam per hour. The cyclone and pulverized boiler systems are
typically designed for power-generating stations and have
greater than 200,000 pounds of steam per hour capacity. Because
of the differences in design of these boilers, their flexibility
in adapting to different coals also varies. Those coal charac-
teristics which determine the acceptability of a new fuel are
directly related to the boiler type and design.
The characteristics of coal which can be important in
successful operation include Btu content, moisture content,
grindability, ash fusion temperature, volatility, and ash con-
tent. These factors are interrelated and influence the boiler
operation in many ways. High moisture coals will have low
Btu content and thus a greater quantity must be burned to main-
tain boiler capacity. Moisture and volatility affect the com-
bustion characteristics in the boiler. Ash content and ash
fusion temperature are important indicators of the possibility
of developing a slag layer for cyclones or of avoiding clinkers
in other types of boilers.
To summarize the operating difficulties and methods of
resolution for various boiler types, Table 1 was prepared. For
each of the five types discussed, the coal characteristic
which is primarily responsible is identified. There may be
other contributing or related factors in addition to the
ones listed; however, the attributes of western coal which
appear to be significant are moisture or Btu content, ash
characteristics, and ash fusion temperature. The major operating
problems encountered were loss of boiler capacity, carbon
carryover, maintaining proper combustion, and ash formation.
The methods of resolving these problems involved equipment
adjustments, increased maintenance costs, and equipment pur-
chases. Thus, there are costs associated with these problems,
but the technological problems can be resolved, or at least
minimized, by applying these techniques.
IIT RESEARCH INSTITUTE
2 IITRI-C6333C04-3
-------
Table 1
TECHNOLOGICAL PROBLEMS OF BOILER OPERATION
Boiler
Coal Type
Coal
Characteristic
Technological
Problems
Method of Resolution
Cyclone
Lignite
High moisture
Loss of boiler
capacity and car-
bon carryover
1. Raise primary and secondary air to
750°F to dry coal
2. Two-stage conditioning to dry coal
3. Bypass moisture around furnace to
increase heat value
Cyclone
Sub-bituminous
Low Btu content
Loss of boiler
capacity
1. Raise primary air to 650°F to dry
coal
Low Btu content
and high moisture
Carbon carryover
1. Adjust crushers to 97% particles
pass through 200 mesh
2. Modify cyclone tubes to prevent car-
bon from leaking into boiler furnace
Ash content and
fusion temperature
Slag formation
1. Refractory coating applied to cy-
clone to increase temperature for
combustion and slag formation
2. One slag tap utilized instead of
two
O
CTi
U>
W
CO
o
o
Pulverized
coal
Lignite
Low Btu content
Higher feed rate
of coal needed to
maintain boiler
capacity
1. Larger motors in pulverizer
2. Increase feeder capacity
u>
-------
Table 1 (cont.)
Boiler
Type
Coal Type
Coal
Characteristic
Technological
Problems
Method of Resolution
Pulverized
coal
(cont.)
Lignite
High moisture
content
Proper ignition and
loss of boiler
capacity
1. Higher air temperatures during
pulverization to dry coal
Sub-bituminous
Low Btu content
Higher feed rate
of coal needed to
maintain boiler
capacity
1. Larger mill capacity
2. Increase feeder capacity
Ash content
Little buildup of
ash on tube sur-
faces exposed to
heat
1. Acid clean boilers every three years
instead of five years
-P-
Deposits on super-
heater pendant
section
1. Increased soot blowing
Underfeed
Sub-bituminous
Low Btu content
Low fuel bed per-
meability and par-
ticle drifting
1. Control particle size of coal
M
H
I
n
CTv
u>
n
o
-P-
Low ash, low
Btu content
High carbon loss
1. Change feed rate, rate of burning,
and air flow
Crossfeed
(traveling
grate)
Lignite and
sub-bituminous
High moisture
content
Proper combustion
and ignition
1. Use arches or overfire air to pro-
mote turbulence of volatile gases
2. Adjust feed rate, bed density,
flame length, and excess air
-------
Table 1 (cont.)
H
Jrt
M
I
O
O>
to
to
UJ
C
c
-P'
I
LO
Boiler
Type
Crossf eed
(traveling
grate)
(cont . )
Spreader
stoker
Coal Type
Lignite and
sub -bituminous
Lignite
Coal
Characteristic
Ash content, ash
fusion temperature,
and heat release
rate
High moisture
content
Technological
Problems
Clinkers
Proper ignition
and combustion
Method of Resolution
1. Control particle sizes and fuel bed
depth for appropriate burning rates
and temperature control
1. Preheat air to 405°F to dry coal
2. Proper sizing of fuel for combus-
tion
-------
3. COAL TYPES AND THEIR IMPORTANT ATTRIBUTES
Although coal may represent one of our greatest energy
resources, the variety of constituents within coal have hampered
its full utilization. Not only is the sulfur content an impor-
tant factor, but also ash content, heat value, volatility,
grindability, and moisture affect design considerations.
Because our study is concerned with the usage of low-sulfur
coal versus existing supplies with higher sulfur contents, it
is important to note the differences between these sources.
These differences affect boiler design and operation and must
be considered in an evaluation of the feasibility of such a
conversion. In the following sections, the pertinent coal
types will be described and compared. Also, an analysis of
the characteristics which impact design will be performed as
the first step in determining conversion requirements.
3.1 Coal Types
Coal varies across the United States according to seam,
county, and state. For our purposes, we shall consider those
coals which have less than 1% sulfur and compare these to
midwestern coals utilized by electric generating stations
and industries in Region V. Low-sulfur coal can be categorized
into four major types as shown in Table 2.
Although anthracite is a low-sulfur coal, none of that
is appropriate for our analysis. Clearly, lignite and
sub-bituminous coals are the primary sources of coal with less
than 1% sulfur. Bituminous coal is also available in this
category, but this coal is very difficult to obtain due to
market competition. Therefore, the characteristics of sub-
bituminous and lignitic coals will be compared to midwestern
coals from Illinois and Indiana. Table 3 presents the basic
characteristics of four midwestern coals in comparison to
the average Rocky Mountain coals.
There are significant differences in average levels of
moisture, heating value, sulfur, and grindability among these
NT RESEARCH INSTITUTE
6 IITRI-C6333C04-3
-------
Table 2
ESTIMATED SULFUR CONTENT DISTRIBUTION
BY COAL TYPE
Coal Type
Bituminous
Sub - b i t uminous
Lignite
Anthracite
Percent of Total
Coal Reserves
46.0
24.7
28.4
0.9
Percent of Total Coal Reserves
with Sulfur Content
S < 1%
13.7
24.6
25.8
0.9
S 1-2%
6.2
0,1
2.6
-
S > 2%
26.2
-
-
-
Source: L. Hoffman, et al.; Survey of Coal Availabilities by
Sulfur Content, NTIS PB 211 505, May 1972.
NT RESEARCH INSTITUTE
IITRI-C6333C04-3
-------
Table 3
COMPARISON OF COAL CHARACTERISTICS
Moisture Content (wt % dry)
Volatile Matter (wt % dry)
Fixed Carbon (wt % dry)
Ash (wt 7, dry)
Total Sulfur (wt % dry)
Pyritic Sulfur (wt % dry)
Organic Sulfur (wt % dry)
Grindability Index
Btu/lb
Rocky
Mountain
Bituminous
7.7
40,3
51.4
8.0
0.92
0.29
0.60
50
11,879
Rocky
Mountain
Sub-bituminous
19.6
40 0
51.0
8.4
0.80
0.22
0.53
51
9,235
Rocky
Mountain
Lignite
36.8
42.7
46.5
10.5
0.96
0.15
0.58
48
6,763
Vermilion,
Illinois
(Bed II, Group 5)
12.2
38.8
40.0
9.0
3.2
-
-
11,340
Gallatin,
Illinois
(Harrisburg No. 5)
4.5
36.6
50.7
8.2
2.8
-
-
13,030
Perry,
Illinois
(Herrin No. 6)
10.2
34.1
45.5
10.2
-
-
-
_
11,390
Greene,
Indiana
(Bed VI)
13.1
34.3
43.0
9.6
3.0
-
-
_
11,180
CO
H Source: L. Hoffman, et al.; Survey of Coal Availabilities by Sulfur Content, NTIS, May, 1972.
M
O
Oo
O
O
-P-
I
u>
-------
coals. Such attributes which create problems in operation are
important, and are summarized in Section 2.2. Note that lignite
is considerably different from the bituminous coals of the
Midwest. The moisture content of Illinois coals varies from
10 to 127o while lignites average 36.870. Heating values are
considerably lower for Rocky Mountain coals, which means
greater quantities must be burned to achieve the same Btu per
hour generation.
Although columns 2, 3, and 4 present the average character-
istics of the coals in this area, there is significant devia-
tion within each category, especially moisture, ash, and
grindability. The standard deviation for the values shown was
approximately 15 to 30% of that reported.
The variation in coal characteristics within a state may
also be significant, depending upon the types of coal available
within that state. In Table 4, the average, minimum, and
maximum values for coal analyses are presented as compiled
from U.S. Bureau of Mines data. The average moisture content,
Btu content, and ash softening temperature are quite different
for Illinois and western coals from Montana. Since Montana
presently represents the largest supply of western coals to
the Midwest, it is important to compare the coals from these
two states. The maximum moisture content in Illinois coals is
227,, while 257, is the Montana average. Allowing for variation,
the boiler operating conditions would be quite different for
these two coals. Ash softening temperature, which is impor-
tant in determining the tendency to clinker, is 2,090°F for
Illinois coals compared to 2,430°F for Montana coals. Thus,
the operating conditions will be different for Illinois and
western coals. The net result of coal quality variations and
different averages is a change in the operating criteria when
western coals are used. The importance of the needed modifi-
cation in operating procedure varies with each boiler type
and is discussed in conversion experiences.
NT RESEARCH INSTITUTE
9 IITRI-C6333C04-3
-------
Table 4
RANGE OF COAL CHARACTERISTICS
(
State
Alabama
Arizona
Colorado
111 inois
Indiana
7owa
Kansas
Kentucky
Missouri
Montana
New Mexico
North Dakota
Ohio
Oklahoma
Pennsylvania
Tennessee
Utah
Washington
West Virginia
Wyoming
Min.
Ave .
Max.
Ave .
Min.
Ave.
Max.
Mm.
Ave .
Max.
Mm.
Ave .
Max.
Min.
Ave .
Max.
Min.
Ave.
Max.
Mm.
Ave .
Max.
Mm.
Ave .
Max.
Mm.
Ave .
Ma->-.
Min.
Ave .
Max.
Min.
Ave .
Max.
Mm.
Ave .
Max.
Min.
Ave .
Max.
Min.
Ave .
Max.
Mm.
Ave .
Max.
Min.
Ave .
Max.
Mm.
Ave .
Max.
Min.
Ave .
Max.
Min.
Ave.
Max.
Characteristic as a Percent of Total Coal Com
Moisture
2.9
4.7
12.5
11.7
4.6
12.9
22.5
4.8
10.5
21.9
8.0
11.4
19.0
9.6
15.6
19.2
3.6
4.6
5.8
2.0
6.1
14.9
11.1
12.1
13.2
8.0
25.4
43.0
11.7
12.7
13.7
33.3
35.1
38.6
3.2
5.9
8.2
1.0
3.5
5.0
1.0
3.7
12.0
1 .8
3.0
3.8
2.8
5.3
8.7
4.8
5.0
5.2
1.5
3.6
8.5
15.5
20.1
23.0
Volatil e
Matter
29.7
37.7
42.0
44.4
37.2
39.6
43.3
35.3
41.0
47.4
38.1
42.7
45.3
38.1
40.9
48.]
36.6
38.5
40. 6
33.6
39.2
45.1
43.7
44.0
44.3
33.0
38.2
42.0
44.1
44.2
44.3
40.1
41.9
44.2
39.1
41 .8
45.2
39.4
42.2
45.0
16.0
33.4
41 .4
29.0
31.0
36.8
40.5
45.2
47.0
36.0
38.0
38.0
29.1
36.4
40.4
41.7
43.4
46.4
Fixed
Carbon
51.9
55.9
62.7
47.1
46.6
51.8
56.1
44.5
49.9
55.7
44.4
47.5
52.4
32.3
41 .0
46.6
48.3
50.5
53.0
48.2
54.3
60.7
46.7
47.1
47.4
44.0
51.1
58.0
46.6
47.6
48.6
46.8
48.3
49.2
45.3
49.7
54.1
47.9
48.7
49. b
46.3
57.0
77.0
51.8
57.3
61.0
44.4
50.1
53.5
46.0
46.2
46.4
53.0
56.7
65.6
47.1
50.8
54.2
Ash
2.5
6.1
14.6
8.5
5.1
8.6
14.6
6.1
9.1
11.5
7.7
9.8
11.6
13.1
18.1
29.6
8.5
11.0
11.3
3.6
7.8
17.7
8.9
8.9
9.0
7.0
10.7
16.0
7.1
8.2
9.3
7.9
9.8
13.1
6.1
9.4
13.6
7.1
9.0
11.0
5.8
9.6
21.0
10.0
11.7
14.6
5.7
7.3
13.6
15.6
15.8
16.0
2.8
7.9
16.5
3.5
5.7
7.9
S
0.6
1 .2
2.0
0.4
0.3
0.6
1 .1
1 .5
2.8
4.3
1.1
3.2
4.5
2.5
4.5
10.0
2.3
3.8
4.8
0.6
2.2
3.9
4.1
0.4
1.0
2.3
0.7
0.4
0.7
1.0
2.1
2.7
3.2
3.5
0.7
2.3
8.1
0.6
1.0
1.2
0.3
0.5
0.8
0.3
0.3
0.4
0.6
1.0
1.6
0.5
0.8
1 .0
H
4.9
5.1
—
—
—
4.0
4.5
4.9
4.9
5.0
5.1
5.3
5.4
5.5
—
4.5
5.2
—
5.1
1.5
4.9
5.1
5.4
4.9
--
;;
4.3
5.1
7.0
5.0
C
76.9
70.3
--
—
—
52.6
62.0
68.7
72.0
72.6
73.3
79.5
E
68.1
70.9
—
74.5
76.8
73.7
76.7
79.5
73.5
—
;;
73.1
80.0
86.6
72.1
N
1.8
1.1
—
—
—
0.9
1 .3
1.6
1.2
1.6
;;
1.0
1.3
—
1.5
1.5
1.1
1.4
1.5
1 .8
—
E
1.2
1.5
1.8
1.6
position
0
8.7
L4.6
—
—
—
4.3
6.6
8.9
3.1
3.7
4.3
7.2
;;
14.7
12.6
—
6.2
5.6
4.8
5.6
6.9
7.2
—
E
1.9
5.3
7.9
4.1
Btu,
°F/lb coal
12,160
13,280
14,150
10,900
10,730
11,050
11,270
10,000
11,780
12,810
10,670
11,540
12,370
8,350
9,580
10,970
8,350
9,580
10,970
11,210
12,800
14,150
11,390
11,530
11,680
7,290
8,680
11.030
10,790
6,700
11,340
12,560
13,440
12,730
13,070
13,420
10,750
13,020
14,420
12,370
12,370
13,350
11,370
11,430
12,850
11,630
11,670
11,720
11,930
13,130
14,390
9,540
10,140
10,700
Ash
Soft r-nmg
Temperature ,
°F
2,130
2,320
2,680
—
2,260
2,910
2,000
2,090
2,180
2,000
2,330
2,700
1,910
2,060
2,200
1,980
2,020
2,070
2,130
2,410
2,800
2,020
2,030
2,050
2,380
2,430
2,490
2,080
2,910
1,990
2,240
2,520
--
—
2,020
2,410
2,910
2 ,080
2,460
2,910
2,110
2,250
2,420
2,590
2,910
2,070
2,540
2,910
2,450
Source.
ttonsanto Research Corp., Evaluation of Low-Sulfur Western Coal Characteristics,
Utilization and Combustion Experience, 1975 .
10
-------
3.2 Attributes of Coal Important to Boiler Design
There are several major coal characteristics which influence
boiler design and operation. These factors determine the rank
of coal and thus its range of usefulness. It is important to
be familiar with the definition of the tests and phrases which
describe various coals. Table 5 summarizes the most useful
of these attributes which are often referred to in later sec-
tions of the report. A general indication of the effect of
these coal characteristics is presented for two major boiler
categories, the stoker and the pulverized coal systems.
Table 6 lists eight characteristics and the impact on design
that these variables have. The pulverized and stoker fuel sys-
tem designs are especially affected by variations in coal ash,
moisture, and volatility. Low-sulfur western coals have sig-
nificantly different characteristics in these respects and
thus affect operation of the boiler system. Any modification
of the coal characteristics from design may substantially
alter operations, depending upon the type. Because there are
many types of boilers within each category, a breakdown and
discussion of these is provided in the next section.
4. GENERAL DESCRIPTION OF BOILER TYPES
A boiler system is comprised of several components, such
as the type of fuel system, coal injection system, and ash
handling facilities. Depending upon the boiler size and the
coal which is to be burned, a combination of these systems is
selected for use. Table 7 summarizes the general categories
and limitations of these systems.
The two types of boiler systems specifically reviewed
during this segment of the project were cyclone boilers and
traveling grate stokers. Clearly, the traveling grate is a
crossfeed system which is generally used for boilers of
6,000 to 200,000 pounds per hour steam. The fuel range is
designated at bituminous, and it is not considered a system
which can accept a wide variety of coal. The cyclone boiler
NT RESEARCH INSTITUTE
11 IITRI-C6333C04-3
-------
Table 5
DEFINITION OF COAL CHARACTERISTICS
Coal
Characteristic i
Definition
r Moisture
Natural moisture lies in pores and is a true
part of the coal, being retained when air
dried, Surface moisture depends on climatic
conditions High moisture content in effect
reduces the heat value of the coal.
Ash
Volatile
Matter
I
.,__, . , ..__.
Fixed
Carbon
Sulfur
Ash is impurities which form the incombustible
matter left behind after burning,
This is the portion of coal driven off in
gaseous form when a standardized temperature
test is performed. This affects firing mech-
anics, and thus furnace volume,
The combustible residue which is retained
after: the volatile matter is flashed off is
the fixed carbon
Three forms of sulfur are found in coal;
pyritic (combined with iron), organic, and
sulfate
!Ash-Fusibility
I Temperature
In a reducing atmosphere, cones of ash are
heated and the temperature at which the cone
fuses down is the "softening temperature",
This indicates clinkering and slagging
tendencies under furnace conditions. Two
other stages in the fusibility test are IT
(initial deformation) and FT (fluid tempera-
_ tur e} _. _.___
Grindability
Caking
Freeburning
This measures the ease of pulverizing coal for
a given amount" of grinding energy. The
higher the index, the more easily it is pul-
verized. _ ^ _^_
Measured by free-swelling index, caking or
non-caking refers to <~he tendency of coal to
agglomerate dxiring burning
I IT RESEARCH I NSTITUTE
12 IITRI-C6333C04-3
-------
Table 6
COAL CHARACTERISTICS AFFECTING BOILER DESIGN
H
m
CO
m
0
CO
— I
— I
c
H
m
Coal Characteristic
Sulfur
Ash
Ash Fusibility
Volatility
Moi sture
Coal Size
Grindability
Boiler Type
Pulverized
Affects slagging and air heater
exit temperatures
Reduces handling and burning
capacity. Retards combustion
Influences choice of furnace
bottom, depending on fusion
temperature „
Low volatile coal ignites less
readily which affects furnace
size and amount of cooled
surface
Reduces burning and handling
capacity Affects ignition
and increases flame length
Pulverizer capacity changed
by sizing needs
Affects mill capacity, cost,
and maintenance
Stoker
Affects clinkering and slag,
Also limits economizer exit
temperatures ,
Reduces handling and burning
capacity
Indicates clinkering or ftising
characteristi cs -
Affects flame length and thus
minimizes grate settling height
and furnace volume,
Reduces burning and handling
capacity
Caking property and particle
size determine the density and
uniformity of fuel bed which
changes air needs
-
LO
o
LO
LO
LO
n
o
I
LO
-------
Table 7
CATEGORIZATION OF BOILERS
Type of
Fuel.System
Coal_ Injection System
Boiler
Capacity (#/hr)
Fuel Bed
1) Spreader or Overfeed
a) Traveling Grate
b) Stationary
c) Reciprocating
d) Vibrating
e) Oscillating
f) Dumping
2) Mass-Burning or Crossfeed
a) Chain
b) Traveling
c) Vibrating
3) Underfeed (Single Retort)
a) Reciprocating Ram
b) Stationary
c) Undulating
5,000-400,000
100,000-400,000
5,000- 30,000
5,000- 75,000
Up to 150,000
5,000- 60,000
6,000-200,000
6,000-200,000
6,000-200,000
Up to 20,000
Up to 25,000
Suspension
1) Pulverization
a) Direct Firing
b) Direct Firing
Circulating
c)
2) Cyclone
Greater than
200,000
Greater than
200,000
Sources: 1.) "Burn Coal in Fuel Beds in Small Industrial
Boilers", Power, March 1974.
2.) Roberson, J., "Selection and Sizing of Coal
Burning Equipment", Power Engineering, October 1974,
IT RESEARCH INSTITUTE
14 IITRI-C6333C04-3
-------
system can be considered a sub-category of pulverized systems
even though the coal is only crushed, not pulverized. Its
usage is primarily large utility and industrial boilers with
great flexibility in fuels burned. These two systems are
discussed in detail in the following section.
5. CYCLONE BOILER
The cyclone boiler is a design adaptation for utilities
which burn lower rank coals, such as those found in Illinois.
Primarily utilized in the Midwest and in the states of North
Dakota and Montana, the cyclone furnace has gained acceptance
and over 700 were in use by 1970.
Before discussing the problems associated with the
conversion from Illinois coals to low-sulfur western coals,
it is important to understand the basic operation of the
cyclone furnace. Therefore, a brief description of the
important operating parameters and design characteristics
related to fuel utilization are presented.
5.1 Cyclone Boiler Operation
In order to circumvent firing and ash-handling problems
associated with lower rank bituminous coals, the cyclone
furnace was developed. The basic principle of operation is
to introduce crushed coal and combustion air tangentially
to impart a whirling motion in the cylindrical horizontal
fxirnace, Figure 1 depicts the coal and secondary air inlets
used to maintain the centrifugal action. Combustion occurs at
temperatures over 3,000°F, which results in a molten ash layer
on the walls of the cylinder. Those gases generated during
combustion exit from the cylinder into the boiler furnace
while molten slag drains out through the slag tap opening.
As coal particles are fed into the system, the centrifugal
force throws the particles onto the walls where they are held
I IT RESEARCH I NSTITUTE
15 IITRI-C6333C04-3
-------
Figure 1
CYCLONE FURNACE OPERATION
Source: Babcock and Wilcox, Steam and Its
Generation, 1972.
NT RESEARCH INSTITUTE
16 IITRI-C6333C04-3
-------
in the slag, burned, and then the ash becomes a molten slag.
It is important for successful operation to maintain air
flow, the furnace temperature, and the slag coating.
There are several auxiliary systems to the cyclone which
will be included in this discussion because of their contri-
bution to the overall performance of the cyclone. Coal is
usually crushed in a preparation plant and then fired or
stored in coal silos. As the coal is fed to the boiler, it
is usually transferred by a conveyor belt to a gravity system
controlled mechanically to insure a uniform feed rate. From
this system the coal enters, burns, and exits as a molten
slag to a holding tank where it is quenched. In Figure 2,
these systems are shown in a typical cyclone furnace con-
figuration.
According to the Babcock and Wilcox Company (1), there
are several important fuel characteristics which affect the
design and operation of the cyclone Volatile matter higher
than 15% is needed to sustain the combustion rate. An ash
content between 6 and 15% on a dry basis is required to
assure a proper slag coating can be obtained. Other important
fuel criteria are the sulfur content and ratio of iron to
calcium and magnesium in the coal, The tendency to form
iron and iron sulfide must be sufficiently low for proper
boiler operation.-
Maintaining a slag layer is of the utmost importance
in sustaining proper boiler operation. At a viscosity of
250 poises, the slag will run horizontally out of the furnace
into the slag tap. The temperature at which this viscosity
is attained depends upon the chemical constituents in the ash.
Each coal has its own fusion temperature, and, thus, the fur-
nace must be controlled to maintain this temperature. With
lower Btu coal, a greater feed rate of combustion rate is
needed to reach the same furnace temperature, and thus the
control of the furnace may be very difficult.
NT RESEARCH INSTITUTE
17 IITRI-C6333C04-3
-------
Attemperator
Reheat
Superheater
\» Gas Outlet
Air Inlet
Figure 2
CYCLONE BOILER SYSTEM DESIGN
Source: Babcock and Wilcox, Steam and Its Generation
1972. '
I IT RESEARCH I NSTITUTE
13 IITRI-C6333C04-3
-------
The moisture of the coal can vary over a wide range,
depending upon the plant's facilities for pre-drying, fuel
preparation, and secondary air temperature. Moisture levels
affect ignition stability and combustion temperature, and
therefore, should be controlled for adequate cyclone perfor-
mances. All of these coal characteristics are considered in
the design and operation of the cyclone furnace.
5.2 Usage of Low-Sulfur Western Coals in Cyclone Boilers
The use of low-sulfur western coals in cyclone boilers has
been considered not only as a converison from other fuels, but
also as a design criterion. There are several examples in the
literature of cyclones designed for lignite and sub-bituminous
coals; however, the number of cyclones which have been con-
verted from bituminous to lower rank coals is limited to two
midwestern utilities, Northern States Power and Commonwealth
Edison. In the following sections, a discussion of the design
and operating parameters which have affected boiler performance
are presented. Methods for improving performance which have
been attempted or considered are listed, as well as the costs
of implementation.
5.2.1 Boiler Design for Western Coals
Cyclone boilers, which were designed for lignite and sub-
bituminous coals, differ from those in which midwestern coals were
burned. The first commercial lignite-fired cyclone was located
at the Black Hills Power and Light Company in South Dakota, and
its design was similar to the standard one. By 1970, several
features were added to the cyclone furnace as exemplified by
the design of the Milton Young Station, Minnkota Power Coopera-
tive, Inc. in North Dakota (2). This station, which was de-
signed to burn lignite up to 40% moisture, utilized the following
modifications:
1. Primary and secondary air at 750°F.
2. Two-stage conditioning system to dry fuel before
combusiton.
NT RESEARCH INSTITUTE
19 IITRI-C6333C04-3
-------
3. Auxiliary fuel for startup or during burning of
low heat value fuel.
4. Some moisture from coal is bypassed around furnace.
Cyclones designed for burning lignites at the Leland
Olds Station and Big Stone Plant, owned by Basin Electric Power
and Ottertail Power Company, respectively, included several
features to aid in operation (2). The upper furnace was
expanded in depth to reduce gas velocities and heat absorption
rates in order to minimize and control slagging. Also
incorporated was gas tempering to control gas temperatures
to a low level entering the superheater„ This modification
allows reheating without accumulating high-temperature ash
deposits.
Boilers burning sub-bituminous coals with moisture con-
tents of 307o in the coal do not require as many adaptations.
In the design of a 600-MW cyclone furnace, Babcock and Wilcox
used the following modifications (2):
1. Primary air at 650°F,
2. Air-lift crusher for each furnace.
3o Convection pass design similar to lignites.
4. All moisture enters furnace.
Thus, it appears that cyclone furnaces which burn sub-
bituminous or lignite coals require modifications from the
standard design in order to operate efficiently. The range
of coals which can be burned within an existing system depends
upon the difference between the original design fuel and the
low-sulfur western coal alternative. In the following section,
the results of such an operating conversion are examined.
5.2.2 Fuel Conversion Experience
Deviation in fuels from the design coal can result in
operating problems within the boiler„ Two pilot tests in
which a range of coals was examined and two full scale
I IT RESEARCH INSTITUTE
20 IITRI-C6333C04-3
-------
operations which converted to western coal provide infor-
mation regarding boiler performance. Each of these studies
and their results are summarized briefly.
1. Black Hills Power and Light Company (3) (Ben French
Station)
Three coals were tested in the cyclone boiler to
ascertain the flexibility in coal characteristics
which could be tolerated. These three coals are
described in Table 8 and varied in heat value from
6,500 to 8,100 Btu's per pound. Cyclone performance
was satisfactory for the design coal and the Baukol-
Noonan coal; however, the Glenharold coal, which
represented the highest moisture, required 570
supplementary fuel to insure ignition. Without the
gas, lighter slag deposits and unburned fuel
accumulated at the bottom, front end of the cyclone
furnace. These deposits resulted in carbon carry-
over into the boiler primary furnace.
2. Babcock and Wilcox - Barbarton Works (3) - Test
Program
Babcock and Wilcox, who is a major designer of
cyclone furnaces, conducted a series of tests using
the high moisture Glenharold coal. Without modifying
their existing boiler, Babcock and Wilcox could not
achieve the desired boiler performance without
adding supplemental gas fuel. Therefore, modifi-
cations of their boiler system were required to
successfully burn a high-moisture low-Btu coal.
By bypassing some moisture from the cyclone and
installing a pre-drying system for the coal boiler,
operation improved. Also, using combustion air at
700-750°F and lower levels of excess air (raises
furnace temperature) aided combustion,
3. Commonwealth Edison (4)
At the 1973 ASME Winter Meeting and in a recent
meeting with IITRI personnel, Commonwealth Edison
representatives discussed their long-term operating
experiences in utilizing low-sulfur, western coals.
The problems encountered related to carbon carry-
over, slag layer formation, and boiler derating.
The moisture, ash, and chemical constituents of
western coal all affected boiler operation. In
Table 9, there is a comparison of three coals which
could be utilized by Commonwealth Edison. Colstrip
coal resulted in explosions in the exhaust ducting
I IT RESEARCH INSTITUTE
21 IITRI-C6333C04-3
-------
Table 8
BLACK HILLS POWER & LIGHT COMPAQ TESTS—TYPICAL ANALYSES
Date
Mme Glenharold
County Mercer
State N. Dak.
Equilibrium Moisture 36.7
Ultimate Analysis, as fired
Moisture 33.4
Carbon 36.4
Hydrogen 2.7
Nitrogen 0.5
Sulfur 0.4
Ash 75
Oxygen 12.1
HHV, Btu/lb £500
Ash Fusibility, F
IDT reducing 1920
ST h = w 2090
ST h = w/2 2100
FT h = '/.» in. 2300
IDT oxidizing 2090
ST 2120
ST 2140
FT 2380
Asn Analysis
SiO, 36.0
AI30, 14 0
TiO, 0 5
FeA 7.2
CaO ISO
MgO 4.8
Na20 f).40
K.O 1.30
Temperature for 250 poises, F 2100
jjne and July 1966
Baukol-Noonan
Burke
N. Dak.
33.3
35.4
42.2
2.9
0.7
0.3
6.9
11.6
7180
1950
2030
2080
2180
2230
2270
2290
2330
30.0
11.0
0.6
6.6
21.0
4.7
11.00
0.64
2120
Wyodak
Campbell
Wyoming
30.6
30.5
483
3.3
0.7
0.4
5.4
11.4
8100
2130
2150
2170
2340
2150
2170
2200
2290
26.0
15.0
1.0
74
22.0
6.4
1.30
0.27
2210
Source: Rusanowsky, N., "Lignite Firing in Cyclone Furnaces",
Proceedings of American Power Conference, 1967
IT RESEARCH INSTITUTE
22 IITRI-C6333C04-3
-------
Table 9
CHARACTERIZATION OF THREE COALS
Coal Characteristic
Moisture Content (%)
Volatile Matter (%)
Ash (%)
Sulfur (%)
Heating Value (Btu/lb)
( IT (°F)
Ash J 0 .
Fusibility ' ST ( F)
FT (°F)
Si02 (% of ash)
Fe203 (% of ash)
Ti02 (% of ash)
P20s (% of ash)
CaO (% of ash)
MgO (% of ash)
Na20 (% of ash)
K20 (% of ash)
S03 (% of ash)
A1203 (% of ash)
Mine No. 10
Christian County
Illinois
12
39.7
16.5
5.0
11,540
1,905
1,945
1,985
43,7
21.3
0.5
0.3
7.0
1.0
1.5
104
6.1
17.0
Colstrip
Rosebud County
Montana
21
39.9
9.7
0.8
11,620
2,190
2,220
2,250
35.4
5.6
0.8
0.3
17.8
4.4
0.3
Ool
16 o 3
19.0
Glenrock
Wyoming
22
45.4
10.0
0.8
11,110
2,120
2,155
2,190
30.5
6.6
0.6
0,4
25 .,5
3.7
0.3
0.5
16.4
15.7
Source: Bureau of Mines Circular No. 8471, Technology and Use of Lignite.
NT RESEARCH INSTITUTE
23 IITRI-C6333C04-3
-------
caused by excessive carbon carryover and was totally
inadequate, while Arch-Mineral coals, which are
similar to the Wyoming coal, have been satisfactorily
burned. Clearly, the differences which appear small
significantly impact boiler operation. High mois-
ture impedes ignition and lowers the furnace tempera-
ture. Due to chemical constituents and ash character-
istics, a satisfactory slag layer may be difficult
to maintain.
To alleviate the carbon loss, Commonwealth Edison
attempted pre-drying of the coal and crushing to
977o through a 1/4 in. sieve. In their test runs, no
significant improvement in carbon loss was achieved.
Carbon carryover can result in fires in the duct
work, air heaters, or precipitators, which is a
signficant maintenance cost and loss of boiler capacity
No major modifications have been made to existing
cyclone systems, such as Waukegan, Will County, or
Stateline, where western coals are currently being
burned. The costs associated with this operation
are boiler capacity derating of up to 207o and
extraordinary replacement of equipment.
Some of the modifications employed by Commonwealth
Edison to improve operations are the following:
a) Cyclone tube modification -- The cyclone re-entrant
throat openings were closed to prevent carbon from
leaking into the boiler furnace.
b) Adjustment of crushers --To maintain better con-
trol of particle size distribution which should
enhance combustion.
c) Secondary air temperature was raised from 600°F
to 700°F to dry coal and improve combustion.
d) Alteration of secondary dampers -- Damper closest
to furnace was closed to prevent carbon entering.
e) Refractory coating was applied to increase the
cyclone temperature.
f) Other changes suggested were an increase in the
pressure drop across the cyclone, excess air at
77o, and a reduction in primary and tertiary air
settings.
4. Northern States Power (5)
Presently, Northern States Power is burning low-sulfur
western coal in their power plants in Minneapolis.
No modifications were made to their existing systems,
IIT RESEARCH INSTITUTE
24 IITRI-C6333C04-3
-------
although Babcock and Wilcox recommended either supple-
mentary fuel (gas) or better particle size control
in their crushing to alleviate operating problems.
5.3 Cost of Utilizing Western Coals
Certain modifications may be required to satisfactorily
burn low-sulfur western coal in a cyclone boiler. Commonwealth
Edison listed several actions which they had taken to improve
operations with low-sulfur coal. These alternations included
crusher adjustment, cyclone tube modification, an increase in
secondary air temperature, and an increase in pressure drop
across the cyclone. The costs associated with these modifica-
tions are difficult to estimate because of the importance of
plant configuration. However, the cost of additional crusher
capacity and the cost of lost boiler capacity due to derating
may be presented as potential costs incurred in converting to
low-sulfur western coal. The additional maintenance and equip-
ment replacement costs cannot be readily included in the calcu-
lations presented, but should also be considered,
5.3.1 Boiler Derating
Conversion to low-sulfur, western coal has reduced the
effective capacity of the cyclone boiler due to the lower
heating value of the western coal and constraints upon feeding
rates. According to Commonwealth Edison (4), in 1973, a
3.670 or 400 mw system reduction for cyclone and pulverized coal
systems was realized because of the use of low-sulfur western
coal. Mill capacity limitations of pulverized coal systems were
responsible for a large portion of this loss (4). The actual
cost associated with a boiler derating varies according to the
operating characteristics of the individual generating station.
IT RESEARCH INSTITUTE
25 IITRI-C6333C04-3
-------
5.3.2 Crushing Equipment
As suggested by Babcock and Wilcox representatives and
the literature, better control of the particle sizing would
improve boiler performance. Rather than requiring 90% of
the particles through 1/4" mesh, 99% must pass through this
screen. To achieve a higher level of particle size uniformity,
additional crusher capacity would be required.
To estimate the cost of using such additional equipment,
a feed rate of 400 tons per hour was assumed. At least 570
additional crushing capacity or 10 tons per hour was required
to maintain the proper feed rate to the boilers. This
modification can be obtained at a cost of $172,000 per unit*,
based on values from Popper's Modern Cost Engineering (6).
5.3.3 Conclusions on Conversion
Presently, the usage of low-sulfur western coal in
cyclone boilers is occurring without any modifications to
the system. To alleviate costly repairs and operation, the
variability in coal quality must be reduced or the cyclone
furnace must be adapted. Changes in coal attributes and
their impact on operation must be thoroughly investigated to
understand the operating difficulties associated with this
fuel conversion. To improve operation, it is possible to
modify a cyclone furnace, coal preparation equipment, or sup-
porting systems, such as ash handling.
6. TRAVELING GRATE STOKER
The traveling grate stoker is a member of the fuel-bed-
fired devices and is generally used in industrial applications.
This stoker was very popular in the 1940's, but its use has
waned since that time. The basic operation of this stoker
is much simpler than the cyclone and will be discussed in
the following sections.
* Updated to January 1975 dollars.
NT RESEARCH INSTITUTE
26 HTRI-C6333C04-3
-------
Utilization of western coal in this particular device
can only be described in general terms because of the lack
of information. Although direct examples of conversion to
low-sulfur coal were not located, references to successful
operation were obtained and are discussed. The modifications
which would insure boiler operation are listed, and their
associated costs are discussed in the ensuing section.
6.1 Traveling Grate Operation
The operation of a traveling grate stoker is primarily
one of dropping coal on a moving grate through a high tempera-
ture region within a furnace. Typically air flows upward
through the grate and is used to burn the coal and volatile
gases emitted. Figure 3 shows the general structure of a.
chain grate stoker which is very similar in design. As the
coal burns, it is not disturbed in the bed, and it finally is
reduced to ash which is collected in a hopper on the far
side of the furnace as the belt rotates.
The burning mechanism in the fuel bed is very important
in determining the furnace's performance. In Figure 4, a
simplified version of the combustion zones in the bed is
depicted. These zones vary in location and shape, depending
upon the feed mechanism and grate construction. As the coal
is ignited, the volatile matter is emitted (distillation
zone). When all oxygen is consumed as the coal burns to
carbon dioxide (oxidation zone), then carbon monoxide is
formed (reduction zone). At the end of the burning process,
only ash is left in the fuel bed. Secondary air is usually
added to aid in achieving complete burning. The fuel bed
temperature depends upon the firing rate of coals, and if the
ash fusion temperature is exceeded in the bed, clinkers may
form. In the chain grate, clinkers are broken as the chain
goes over the drum with a scissor-like action; however, there
is no such motion in the traveling grate, and thus, clinkers
may be problem in operation. The rate at which fuel is
IIT RESEARCH INSTITUTE
27 IITRI-C6333C04-3
-------
GATE OPERATING
MECHANISM
GIRDERS I I I- ^ * ^
_]__ _ J ~ I SIDE WALL WATtR BOX
ijgFBrtu jitflfciiilJli Jii^i ju il/i'jj^,.;'J-J.'i iU_ii. . / •„_ "
j^ir— *sj-- -, - i» » fa *„ *fy*-S.T^
O I »j JuIE^Sfel
MR ENTRY TO COMPARTMENTS^
SIFTINGS HOPFER
Figure 3
CHAIN GRATE STOKER CONFIGURATION
IT RESEARCH INSTITUTE
28 IITRI-C6333C04-3
-------
+ No + H00
z z
CO + 'A 2 + '$2 + H2° + Hydrocarbons
Secondary Air
Primary Air
1
Distillation-
Reduction
Oxidation
Ash
Figure 4
SIMPLIFIED FUEL BED DIAGRAM
NT RESEARCH INSTITUTE
29 IITRI-C6333C04-3
-------
burned depends upon the heating value, bed thickness, and
grate speed. Control of these variables allows the stoker
to adapt to a variety of loads and fuels.
The amount of ash within a coal may also affect operation
in that coals with less than 7% ash do not sufficiently pro-
tect the grates from overheating and cannot be used. Higher
ash coals may tax the capacity of the ash handling system
and lead to an expansion problem.
Another variable which is important is the control of air.
Air pressure may vary from section to section on the grate to
control combustion and heat release. If preheated, the
temperature must be regulated to prevent clinkers.
^•^ Usage of Western Coals in Traveling Grate Stokers
According to Babcock and Wilcox (1), the traveling grate
stoker represents a versatile process which can handle a
variety of fuels from wood to bituminous coal. Other reports
also indicate that traveling grates can burn western coals
without difficulty. Modifications of these systems, in order
to burn western coals, have not been discussed in the avail-
able literature„
As early as 1951, there were reports of traveling grates
burning lignite without difficulty. Stokers in North Dakota,
Wyoming, Minnesota, Canadian Alberta, and Saskatchewan were
more conservatively designed for lignite coals than other
midwestern fuels (8)„ Another report (9) on traveling grate
operation in 1951 also indicated successful performance
without additional coal preparation. Designs for these fuels
differ from the standard stoker which does indicate that some
operating problems may be incurred by switching fuels„
A design consideration in using western coals is the use
of arches or overfire air to maintain ignition and combustion
(9,10). This is especially useful for the high moisture
NT RESEARCH INSTITUTE
30 IITRI-C6333C04-3
-------
lignite fuels. The ash fusion temperature is different for
western and midwestern fuels as shown in Table 8. This differ-
ence requires that the heat release rate, coal feed rate, excess
air, and flame travel all be adjusted. Figure 5 depicts these
design criteria for various coal types. Maintaining proper
fuel bed thickness is also important in controlling the rate
of combustion and preventing clinker formation. If the heat
release rate is too high, the ash may form clinkers because it
was not sufficiently cooled.
Coal sizing for a traveling grate varies, depending upon
the rank of coal. Therefore, according to ASTM Classification,
an Illinois bituminous of Rank II-4 or II-5 and sub-bituminous
coals of III-l, III-2, and III-3 should have 50% through a
1/4 in. screen. The grindability index for the Illinois and
sub-bituminous coals does differ, and adjustments in the
crushing equipment would have to be made to obtain the correct
particle size and decrease the number of fines. This would
also reduce the clinker problem.
To reduce clinkers, which is one of the major problems
with western coals, requires changes in operating parameters,
such as bed density, flame length, and air requirements.
Expenses involved in such adjustments are difficult to estimate
because the corrections are basically in-process and no data
regarding such changes is available.
7. UNDERFEED STOKER
The underfeed boiler is primarily utilized for heating
and in small industrial facilities. Approximately 70% of the
boilers designed for 10,000 to 16,000 pounds per hour of steam
are underfeed boilers (10). Since primary emphasis of the
project is large utility and industrial boiler types, only a
brief description is provided of this operation and expected
problems.
NT RESEARCH INSTITUTE
31 HTRI-C6333C04-3
-------
Figure 5
STOKER DESIGN CRITERIA
Ash softening temperatur^ (redur.r.g atmosphere) °F l?nO 2200 4 a.>ove
Grate heal release rate - Bcu Inpa'/hour/uq ft grat.« arf>a 300-I42S.OOO 'tSO-SGO.OOO
Orate coal feed rate - pounds/hour/foot it oker width See diagram A
Furnace heat liberation - ctu ln;.ut,'hour/cu ft furaaci? vol. 35-UO.uOO jO-3%000
Flame travel - (distance from grates to furnace exlt^ feet Approx 1? 10-
IOWER
25 M> 75 100 iX) 200
BOIIiR CAPACITY, pounfls steam iar hour X 1000
250 10 J50
f,fi*IE MtAI RtLE*S£, BTU (
<00
R i
Source: Table 40, Monsanto Research Corp., Evaluation of
Low-Sulfur Western Coal Characteristics, Utiliza-
tion, and Combustion"1975.
IIT RESEARCH INSTITUTE
32 IITRI-C6333C04-3
-------
7.1 Underfeed Stoker Operation
The basic design of the underfeed stoker is to feed coal
into the fuel bed from below. Coal in a feed trough overflows
onto the bed because of the pressure of fresh coal feed behind
it, and then the coal is combusted on the fuel bed as shown in
Figure 6. The rate of burning depends upon the type of coal
utilized and its ash softening temperature as well as the air
distribution system (10). Usually the main air chamber is
directly below the retort and air is forced through holes in
the grate bars.
7.2 Usage of Lew-Sulfur Western Coals
To operate an underfeed stoker with low-sulfur western
coal requires strict regulation of coal particle size. By
limiting coal to the following three sizes, particle drifting
and low fuel bed permeability caused by fines can be prevented:
1-1/4 in. x 3/4 in. -- nut
3/4 in. x 5/16 in. -- pea
507o passes 1/4 in. hole -- slack
High carbon losses which reduce boiler capacity can also
be expected for low ash, low heating coals, such as the western
type. The primary modification to correct these two operating
problems is closer scrutiny or higher quality control of coal
size specification (1). Additional changes which are practicable
have not been located in the literature for these small boiler
types.
8. SPREADER STOKERS
One of the more popular industrial boiler designs is that
of the spreader stoker. Fifty percent of the boiler capacity
rated at 101,000 to 250,000 pounds per hour steam is designed
as spreader stokers as well as 30% of the industrial boiler
capacity for those between 251,000 and 500,000 pounds per hour
steam (10). The popularity of this boiler type is attributed
IIT RESEARCH INSTITUTE
33 IITRI-C6333C04-3
-------
Figure 6
UNDERFEED STOKER
Source: Combustion Engineering, Combustion
Engineering, 1969.
NT RESEARCH INSTITUTE
34 IITRI-C6333C04-3
-------
to its ability to adapt to rapid load swings and fuel types.
There are approximately six grate variations in this design which
include traveling grate, chain grate, oscillating, vibrating,
reciprocating, and dumping grate. The operation of the spreader
stoker is basically the same regardless of the grate mechanism
and is briefly described in the folloxtfing section.
8.1 Spreader Stoker Operation
A spreader stoker consists of three basic units, a coal
injection system, stoker grate, and ash handling system.
Usually coal is fed from the fuel hopper info a bladed rotor
which spreads the fuel in the furnace as shown in Figure 7A.
The coal particles are distributed in the furnace according to
size as the overthrow rotor ejects them into the furnace. The
fines burn in suspension while larger particles fall onto a
grate and are combusted there. As the grate, which can vary in
design from a traveling grate to an oscillating one, moves
toward the ash hopper, the fuel bed burns to ash. Air flow
between the openings in the grate and the ash layer protect
the metal parts from reaching high temperatures. The air must
be carefully controlled to prevent disruption of the fuel bed
layers and maintain combustion. Additional air (overfire air)
enters over the bed to maintain the volatile gas turbulence
for proper mixing and combustion. Shown in Figure 7C is the
location of overfire air ports, which are important for enhan-
cing combustion efficiency.
Several types of grates may be utilized with the spreader
stoker, depending upon the plant operation (11). Small
stationary grates are the minimal cost design and require
manual cleaning of ashes. However, these are not commonly
specified today because of air pollution restrictions. Contin-
uous cleaning grates such as the reciprocating, oscillating,
and traveling grate are currently much more popular.
The reciprocating grate, which has a synchronized move-
ment of fuel, air supply, and ash, can supposedly burn
IIT RESEARCH INSTITUTE
35 IITRI-C6333C04-3
-------
m
to
m
O
c
—I
m
M
M
H
i
O
CT>
LO
LO
U>
n
o
-p>
i
©
o
A. General Operation
Coal Hopper
Ash Door
Reciprocating
Feed Plate
Spill Plate
Overthrow Rotor
-_. __ _...__
Stoker Chain
Air Seal
B. Stoker Equipment
Figure 7
SPREADER STOKER DESIGN
-------
Coal Hopper
Overfire
Air
Overthrow
Rotor
Air Seal
Air Seal
<#*-
?SL~>
7
C. Air Source Location
Figure 7 (cont.)
Source: Monsanto Research Corp., Evaluation of Low-Sulfur
Western Coal Characteristics, Utilization and
Combustion,1975.
NT RESEARCH INSTITUTE
37 HTRI-C6333C04-3
-------
bituminous through lignite coals without preparation other than
sizing changes. The traveling grate is utilized in larger
boiler designs and also can handle a variety of coals.
Because the coal is injected into the furnace, the flyash
carryover is high and a reinjection system (pneumatic or gravity)
may be used. For steam capacity above 70,000 pounds per hour,
the gravity type, which directs ash from a hopper onto the
grate, is used (12) to increase boiler capacity 2 to 3%. A
pneumatic system which blows the suspended flyash into the fur-
nace is also frequently used in boiler systems.
The most important parameters for maintaining satisfactory
stoker performance are coal sizing and moisture content (10).
It is important to have a range in particle size in order to
develop a uniform fuel bed. The more fines which are introduced,
the greater is carbon carryover. Large coal particles cause
uneven fuel bed burning and result in clinker formation. If
the coal has high surface moisture, it sticks to the feeder
surface and causes uneven distribution of coal particles. Mois-
ture which is natural to the coal, such as lignites, does not
cause this problem.
8.2 Usage of Low-Sulfur Western Coals in Spreader Stokers
The use of low-sulfur western coals in spreader stokers has
been investigated for a comparison of operation efficiencies.
A discussion of the design and operating parameters which were
affected are presented in the following section, and methods
for improving performance have been listed.
8.2.1 Stoker Design for Western Coals
The spreader stoker is recognized for its ability to burn
a wide variety of fuels; however, in converting from midwestern
to low-sulfur coal, several problems should be considered. The
following three changes or modifications may be necessary to
satisfactorily burn these coals:
1. Higher inlet air temperatures
NT RESEARCH INSTITUTE
38 IITRI-C6333C04-3
-------
2. Crushing equipment adapted or increased
3. Adjustment of flame length
In utilizing lignite coals, the high moisture content re-
quired a higher inlet air temperature for improved handling and
combustion of the coal. Although lignites have more moisture
than sub-bituminous coals, this modification may still be impor-
tant for these coals. Obtaining a distribution of coal particle
sizes is important in obtaining a uniform fuel bed. If too
many particles fall in the same grate portion, then burning is
uneven and clinkers form. The grindability of western coals is
lower than that of midwestern fuels, and therefore, adjustments
in crusher operation are needed. Reduced capacity of crushes
will probably occur because of the more stringent sizing re-
quirements and additional units may be required (10). The
flame length, which was the third adjustment utilized, was
deemed necessary to distribute heat absorption uniformly.
Not many experiences with spreader stokers have been docu-
mented in the literature but one which is particularly detailed
is described in the following paragraph.
1. Minnkota Power Cooperative (Grand Forks, North
Dakota) (9)
In 1951, the first attempt to burn lignite in spreader
stokers was documented. Using a completely open furnace
in an installation of 72,000 pounds per hour of steam,
boiler efficiency of 80% was attained. The design included
economizers and air preheaters because of the high moisture
(~407o) of the coal. Maintaining preheated air at 405°F was
considered critical to achieve optimum operation. A recom-
mendation was made to lengthen the flame mass in some cases
to uniformly distribute heat absorption. The spreader sto-
ker is sensitive to poor fuel sizing which affects operation
by causing fluctuations in operating conditions.
8.2.2 Cost of Utilizing Western Coals
The cost of converting a spreader stoker for burning low-
sulfur western coal is difficult to estimate. Adjustments in
the flame length, air flow rate, air inlet temperature, and
grate speed are basically in-process changes on which no cost
NT RESEARCH INSTITUTE
39 HTRI-C6333C04-3
-------
data are available. Other modifications may also be required
depending upon the ash handling system, grate design, and other
specific design criteria.
9. PULVERIZED COAL FURNACES
Although the first industrial application of pulverized
coal occurred in 1895, in the cement industry, usage of pul-
verized coal in -central power stations did not substantially
increase until after World War I. Primarily utilized in the
electric generating industry, pulverized coal furnaces generally
have a capacity greater than 200,000 pounds per hour stream.
The popularity of this design is attributed to its ability
to handle a wide range of loads and different fuel types.
Operation of these units with a variety of fuels has been des-
cribed in various reports and will be summarized herein. It
is important, however, to understand the basic operation of a
pulverized unit and the possible variations in design. In
the following section these configurations are delineated and
compared.
9.1 Pulverized Furnace Operation
The operation of a pulverized coal furnace relies upon
the suspension burning of extremely fine coal particles, which
makes it quite different from a stoker operation. Basically
fine particles, which are injected into the furnace, are heated
and the volatile matter distilled off. Primary air mixes with
the particles to sustain combustion of the volatiles which
heats the remaining carbon to complete combustion (2). To
operate this system requires a pulverizer to reduce coal to
fine particles, a coal feeder, burners, and an air system as
shown in Figure 8.
There are in general three types of pulverizing or grinding
mills, three burning arrangements, and four types of burners.
The three types of mechanisms used to reduce particle size in
mills are impact, attrition, and crushing. The four most com-
monly used are the ball, ring roll, ball race, and impact
NT RESEARCH INSTITUTE
40 IITRI-C6333C04-3
-------
Bo.le
Secondary ^
sir duct
Primary air '
\to cool
_!/
Pulverizer-^ [H| /4
Burner
Feeder
Figure 8
PULVERIZED COAL SYSTEM
Source: Elonka, A., Standard Boiler Operator's
Questions and Answers, 1969.
NT RESEARCH INSTITUTE
41 IITRI-C6333C04-3
-------
attrition type. The members of the ball mill, ball-and-race,
and roll-and-race pulverizers, are utilized in power generating
stations and industrial applications. Coals which can be
utilized in these pulverizers are identified in Table 10.
Illinois coals which are generally bituminous high volatile
"B" or "C" can be pulverized in all types except impact mills
for "C" coals. Western coals are sub-bituminous or lignite
coals and should be handled by ball-and-race and ring-and-roll
mills. Sub-bituminous "A" and "B" can also be fined in ball
or tube mills. Thus, there is a limitation in design as to
the coals which can be handled. The most important parameters
are grindability index and quantity of coal.
Burners are utilized to insure stable ignition, effective
control of flame shape and travel, and complete mixing of air
and fuel (2). Various types of burners can be required depen-
ding upon the fuel and furnace design. The arrangement of the
burners may be long-flame, shelf system or tangential system
firing. The difference in configuration is the relative place-
ment of the primary and secondary air, as shown in Figure 9.
The coal characteristics which affect pulverizer capacity
and combustion efficiency are the grindability index, surface
moisture, and coal fineness required. When coals of lower
heat value are burned, then the boiler capacity is reduced if
the same pulverization rate is maintained. The grindability
index indicates the ease of pulverization and higher indices
result in greater mill capacity. Western coals have lower
grindability and thus reduce mill capacity although it is not
a directly proportional relationship. Particle fineness required
depends upon the ignition and swelling characteristics. High
volatile contents in coal, such as bituminous, require less
fine particles than low volatiles (western coal). This fine-
ness requirement also affects mill capacity. The relative
effect of fineness and grindability on capacity is shown in
Figure 10.
NT RESEARCH INSTITUTE
42 HTRI-C6333C04-3
-------
Table 10
TYPES OF PULVERIZING MILLS FOR VARIOUS MATERIALS
Type of Fuel
Low volatile anthracite
High volatile anthracite
Bituminous coal (L.V.)
Bituminous coal (M.V.)
Bituminous coal (H.V. "A")
Bituminous coal (H.V. "B")
Bituminous coal (H.V. "C")
Sub -bituminous coal "A" *
Sub -bituminous coal "B" *
Sub-bituminous coal "C" *
Lignite *
Brown coal
Appropriate Pulverizer Type
Ball or
Tube
X
X
X
X
X
X
X
X
X
--
--
--
Impact or
Attrition
--
--
X
X
X
X
--
--
--
--
--
X
Ball
Race
--
X
X
X
X
X
X
X
X
X
X
--
Ring
Roll
--
X
X
X
X
X
X
X
X
X
X
--
* These coals represent typical low-sulfur western coal types,
Source: Combustion Engineering, Combustion Engineering, 1969
IIT RESEARCH INSTITUTE
43 HTRI-C6333C04-3
-------
Pr T;ry
cu
J.-J.'!
Long-fisme system She,? system
~N ' v
,,' 'P^>3
\;^-'-T'*
'Y- -'-_v. '
P' ~crv s^-
cir 'i*
)
Ndary
air
•>*
\ ^
• 'Cff~- ^"
i$$$
•'-' N**
•j> ^
Gorier system
Figure 9
FIRING CONFIGURATIONS OF PULVERIZED COAL FURNACE
NT RESEARCH INSTITUTE
44 IITRI-C6333C04-3
-------
100
95
35
•40 50 60 70 80 50 IOO ilO 120 130 140 ISO 160
PE.R CENT CAPACITY
Figure 10
MILL CAPACITY VERSUS FINENESS AND GRINDABILITY
Source: Combustion Engineering, Combustion Engineering,
1969.
NT RESEARCH INSTITUTE
45 HTRI-C6333C04-3
-------
Moisture of coal can cause agglomeration of fines and only
by using hot air in the system is this problem eliminated. De-
pending upon the total moisture content of the coal, different
air inlet temperatures and flow rates are required. At a flow
rate of 3 pounds of air per pound of coal, coal with total
moisture of 10% required temperature of 300°F while a 26%
moisture coal needed 570°F as an inlet air temperature. Thus,
total moisture is important in ascertaining proper air tempera-
ture and mill capacity for grinding.
9.2 Usage of Low-Sulfur Western Coals in Pulverized
Coal Units
9.2.1 Pulverized Coal Boiler Design
The conversion to and design for western fuels in pul-
verized coal boilers has been performed by utilities in the
Midwest. To accomplish such a feat required several modifica-
tions of existing systems. These can be summarized briefly
to provide an indication of changes needed.
1. Larger motors in the pulverizers are required.
2. Higher air temperatures during pulverization.
3. Increase in feeder capacity.
4. Increased acid cleaning of boilers and maintenance
to pulverizers.
5. Increased number of sootblowers.
These modifications were necessary due to the lower heat
value, higher moisture content, grindability, and ash charac-
terisitcs of western coals. Several experiences with lignite
and sub-bituminous coals are presented in the following para-
graphy to provide an understanding of the importance of these
factors.
1. Crookston Station, Otter Tail Power Company (9)
In 1945, the first pulverized coal unit to burn
lignite was designed. At 75,000 pounds per hour
steam, the capacity of this unit was smaller than
today's designs. Their design included two air
MT RESEARCH INSTITUTE
46 IITRI-C6333C04-3
-------
preheaters to raise primary air temperature to
700°F. No auxiliary fuel was required for ignition
and even at 20% of maximum load, no instability was
noted. The auxiliary power requirements for
grinding were 4.78% of gross power generated or
0.021 Kw per pound of coal processed.
2. Leland Olds Station, Basin Electric Power (13)
A pulverized coal unit which went into operation in
1966 had several design modifications to properly
handle the lignite used as fuel. The 216-mw plant
had six specific design features:
1. increased boiler size by 30%
2. increased pulverizer capacity
3. inclusion of air heaters in the primary air
flow
4. wide separation of pendant boiler tubes to
prevent bridging by ash
5. more thermoprobes than usual to monitor tem-
peratures
6. 100% more sootblowers than same plant with
bituminous coal
The tendency of the ash to build up in boiler gas
passages was solved by wider separation of boiler
tubes. Also, to reduce plugging between superheater
tubes, additional soot blowers were added. Lignite
caused slagging problems because the mills could
not grind to the proper fineness at a sufficient rate
Thus, the low grindability of lignite caused a coarse
grind which induced slagging and carbon carryover.
This problem was solved by increasing the motor horse-
power on mills by 50%.
3. Commonwealth Edison (4)
Commonwealth Edison has utilized sub-bituminous wes-
tern coals in pulverized coal boilers which were de-
signed for Illinois coals. The conversion has re-
quired several adaptations of equipment for success-
ful operation The boiler capacity has been reduced
by 5 to 10% because of mill capacity constraints and
the lower heating value of western coals. Boiler
tubes require acid-cleaning every three years rather
than every five years. Sootblowers are increased in
number and usage frequency. The advantages of wes-
tern coals are that the boiler fire-exposed sections
remain clean, clinker grinders can be eliminated,
and less frequent removal of ash. There are problems
in dewatering ash of western coals and removing it.
NT RESEARCH INSTITUTE
47 HTRI-C6333C04-3
-------
9.2.2 Conversion Costs of Pulverized Coal Boiler
for Western Fuels
The costs of conversion can be estimated for various capi-
tal investment and operating expenses incurred, but the actual
overall cost may be far greater depending upon the specific
constraints and facility modification expenses which accompany
such adaptations. Without additional detailed information,
cost estimations would be inappropriate and misleading.
10. WESTERN COAL AVAILABILITY
The feasibility of burning western coals depends not only
on the technological problems but also upon the supply avail-
able for use. In the early 1900's, coal supplied 887o of the
energy requirements in the United States; however, that dropped
to 177o by 1972. The increased interest in energy independence
has stimulated the demand for coal. Because of the capital
intensive aspects of this industry, however, it is not possible
to respond to rapid changes in demand. Environmental legislation
has also hampered the development of western coal reserves.
The western coal market is quite different from the estab-
lished eastern and midwestern markets. Because of the large
capital investment (approximately $21 and $61 million for a
1 and 3 million ton per year strip mine, respectively), long
term contracts are needed in the development of western coal.
The spot market is a viable organization in the Midwest and
East; however, small operators and excess coal supplies which
create this market in the East are not present in the West.
Sixty percent of western coal production is attributed to
13 mines in 1973. The total number of western coal mines in
1972 was 64, and they produced 51 million tons of coal.
Thus, the supply response to increased demand for western
coal has been rather slow. Manufacturers of mining equipment
normally have a two-year lead time, depending upon market
conditions.
NT RESEARCH INSTITUTE
48 HTRI-C6333C04-3
-------
Transportation equipment, such as barges and railroad cars,
typically require 18 months (14) for the construction of new
equipment. Therefore, the expansion of supply is a planned and
projected affair.
Projected supplies of federal western coals which are 35%
of the total coals by 1980, are shown in Table 11. According
to this forecast, the only midwestern states receiving these
western coals are Iowa, Illinois, Wisconsin, Michigan, and
Minnesota. Another projection of total production for five
western states is presented in Table 12. According to these
predictions, the supply of western coal will double before
1980 (10). Another study by the Federal Energy Administration
(14) (FEA) indicated the following ranges for 1977 and 1980
production:
Millions Tons Per Year
Low Production High Production
Estimate Estimate
1977 81 117
1980 120 213
The FEA study considered possible constraints and is
perhaps a realistic range of production. Most of the western
coal presently supplied is on long-term contract to utilities.
The economies of scale in surface mining have resulted in
large mine facilities with high capital investment. Thus, an
assured customer on contract is needed to develop these mines.
To place the supply projections in perspective relative
to the needs of utilities in the Midwest, the present status
of Commonwealth Edison is described. Table 13 depicts the
coal usage of Commonwealth Edison plants in 1972. The total
coal consumption was 11.2 million tons per year for the plants
shown. In 1973, of the 20.5 million tons of coal under contract
by Commonwealth Edison, 7.5 million tons were western coals.
Table 12, which shows federal coal projections for 1980, indi-
cates 6.9 million tons will come to Chicago, and this does not
NT RESEARCH INSTITUTE
49 HTRI-C6333C04-3
-------
Table 11
PROJECTED COAL PRODUCTION FROM FEDERAL
SURFACE COAL MINES FOR STEAM ELECTRIC PLANT FUELS
FOR 1980-1981
State
Colorado
Montana
North Dakota
New Mexico
Utah
Wyoming
Grand Total
Major Contracts
Location of Mine Annual Tons Location of Powerplant
Oak Creek
Hayden
Craig
Sub-total
Colatrlp
Colstrip
Coir, trip
Colstrip
Colstrip
Colatrlp
Colstrip
Colstrip
Savage
Decker
Decker
Decker
Sub-total
Beulah
Beulah
Gascoyne
Stanton
Center
Zap
Sub-total
Fruit lane!
Gallup
Sub-total
Alton
Sub-total
Qlen Rock
Hanna
Hanna
Hanna
Hanna
Point Forks
Kemmeror
nillPti e
01 lletre
Olllef e
Gillette
Gl iletff
QiilRttP
Glilett.e
Gillette
Glllet-te
Dillette
Sub-total
800,000
1 ,000,000
6JO,ooii
?,"iioo,ooo
2«0,000
8.10,000
1,6.00,000
9^0,000
I,2'i0,0l\.-
1 ,200,00(1
1, 500,000
2,200,000
90,000
5,300,000
6, 500, 000
8,3f n,ooo
£9,890,000
200,000
IbO.OOO
250,000
1,000,000
100,000
i.03.,000
2,510,000
3,&n.|,QOO
<^_u222
T, Bio, ooo
5,600,000
rr^Tooo
3,500,000
100, JOO
1, 3^0,000
1,200,000
u,5'jo,oon
3,000,000
?50,000
cvn,ooo
i.noc ,noo
2, 'in , fion
3,500,000
6,1)0 ,000
3,7''",00n
1,800 ,000
l.Oi • ,000
1, 700,000
5.1^.0;, ^poo
5i, '7n,o"6o
85, ^.H), 000
i-enver, Colorado
Hayden, Colorado
Crals, Colorado
Hill Ings, Montana
Mlnneepolis, Minnesota
Chloa^o, 1 1: Inols
Wlsconslri
"L. Paul, Minnesota
Colstrip, Montana
Cohabsel , Minnesota
Becker, Minnesota
Sidney, Montana
Chicago, Illinois
St Clair, Michigan
American Electric Power
(Locations Unknown)
Hoot Lake, Minnesota
Beulah, Mandar. , N.D.
Ortonvllle, South Dakota
Stanton, North Dakota
Center, North Dakota
Stanton, North Dakota
Fruit land, New Mexico
Joseph City, New Mexico
Las Vegas , Nevada
St. George, Utah
nien Rock, Wyoming
Denver, Colorado
SI nux City, Iowa
Council Bluffs, Iowa
Nebraska
Point of Rocks, Wyoming
Kpmmerer, Wyoming;
Rapid C1t,y, Soutvi Dakota
Gillette, Wyoming
Puet lo, C >lorado
Av • nger , Texas
Toi f-ka, Kansas
Mu^kigee, Oklahoma
Wentern Nebraska
Amarlllo, Texas
Lo . ) si ana
Recilleld, Arkansas
Source: Monsanto Research Corp., Evaluation of Low-Sulfur
Western^Coal Characteristics, Utilization and
Combustion Experience"ID75.
NT RESEARCH INSTITUTE
50 HTRI-C6333C04-3
-------
Table 12
ANNUAL COAL PRODUCTION (1969-1972) WITH ESTIMATES FOR
1973, 1975, 1980, AND 1985
Production
-i
70
m
CO
m
>
Ul *?
M I
z
H
H
C
H
m
State
Arizona3
Montana
New Mexico
North Dakota13
Wyoming
Totals
aForecast by Arizona
1969
.0
1.0
4.5
4.7
4.6
14.8
Bureau
1970
0.
3-
•f
i •
5.
7.
23.
1
4
4 .
6
2
7
of Mines,
1971
1.1
7-1
8.1
6.1
8.1
30.5
1973
in Millions of Tons
1972
1
8
8
6
10
35
.1
.2
-2
.8
• 9
.2
1973
2
9
9
7
13
43
• 9
.9
• 3
.4
.6
.1
1975
10
19
17
11
22
81
.0
.8
.0
.7
.9
.4
1980
13.
41.
27-
19.
87-
187-
0
0
0
0
0
0
1985
13.0+
74.0
27.0+
49.1
140.0
303-0
^ Forecast by Northern Great Plains Resource Program (most probable), 1973
H
^ °Forecast by New Mexico State Bureau of Mines and Mineral Resources, 1973
o
O"\ fj
w Forecast by Wyoming Geological Survey, March 1974
uo
o
o
-p-
Source: Monsanto Research Corp., Evaluation of Low-Sulfur Western Coal
Characteristics, Utilization and Combustion Experience, 1975.
-------
Table 13
COMMONWEALTH EDISON
COAL FIRED GENERATING
STATIONS
Station
Fisk
Crawford
Waukegan No. 1
Joliet
Powerton
Dixon
Stateline
Total
Estimated
tons/year
720,000
930,000
2,131,000
3,819,000
1,114,000
291,000
2,192,000
11,197,000
Source of Coal
Montana and Wyoming
Montana and Wyoming
Illinois, Kentucky,
Wyoming, and Wisconsin
Illinois and Montana
Illinois and Montana
Illinois, Indiana,
Kentucky , Wyoming , and
Wisconsin
Illinois, Indiana,
Montana, and Wyoming
Source: Monsanto Research Corp., Evaluation of
Low-Sulfur Western Coal Characteristics,
Utilization and Combustion Experience,
1975.
NT RESEARCH INSTITUTE
52 IITRI-C6333C04-3
-------
include the 2.2 million tons per year of coal produced by Arch
Mineral (4). The amount of western coal which may become
available between 1975 and 1977 is difficult to project because
of the financial, environmental, and equipment constraints dis-
cussed. Presently, demand exceeds the available supply of wes-
tern coal. Expansion is anticipated, but the explicit commit-
ments to western coal usage are needed at least two years in
advance of obtaining any large supply of western coal.
NT RESEARCH INSTITUTE
53 IITRI-C6333C04-3
-------
REFERENCES
1. Babcock and Wilcox Company, Steam, Its Generation and Use,
New York, 1972.
2. DUzy, A. and Rudd, A., "Steam Generator Design Considera-
tions for Western Fuels", Proceedings of the American
Powder Conference, p. 554-562, 1971.
3. Rusanowsky, N., "Lignite Firing in Cyclone Furnaces",
Proceedings of the American Powder Conference, pp. 475-486,
1967.
4. Commonwealth Edison, "Burning Western Coals in Northern
Illinois", 1973 ASME Annual Winter Meeting, 73-(WA/Fu-Y).
5. Personal Communication with J. Trier, Service Manager of
Babcock and Wilcox Co.
6. Popper, H., Modern Cost-Engineering Methods, McGraw-Hill
Book Company, New York, 1970.
7. U.S. Atomic Energy Commission, 1000 mwe Central Station
Power Plants Investment Cost Study, Oil-Fired Fossil
Plant, Contract No. AT(30-1)-3032. June. 1972.
8. Hoffman, J. and Drabelle, J., "Operation of Large Power
Boilers with Lignite Coals From the Dominion of Canada
and Northern United States", 1951 ASME Fall Meeting,
Paper No. 51-F-18.
9. Pistner, L., "Basic Elements of Design and Operation of
Steam-Generating Units for Utilization of North Dakota
Lignites", 1951 ASME Fall Meeting, Paper No. 51-F-20.
10. Monsanto Research Corporation, Evaluation of Low-Sulfur
Western Coal Characteristics, Utilization and Combustion
Experience, National Technical Information Service,
PB-243 911, May, 1975.
11. "Burn Coal on Fuel Beds in Small Industrial Boilers",
Power, March, 1974, pp. 30-36.
12. Roberson, J., "Selection and Sizing of Coal Burning
Equipment", Power Engineering, October, 1974.
13. Peck, R., "Design Features of Leland Olds Power Station",
U.S. Bureau of Mines, Information Circular No. 8376.
14. U.S. Federal Energy Administration, Project Independence -
Coal, Government Printing Office, November, 1974.
NT RESEARCH INSTITUTE
54 HTRI-C6333C04-3
-------
DISTRIBUTION LIST
No. of Copies Recipient
10 Engineering Investigating Section
Air Enforcement Branch
Enforcement Division
U.S. Environmental Protection Agency
Region V
230 S. Dearborn
Chicago, Illinois 60604
Attention: Mr. Steve Rothblatt
Project Officer
5 Susanne S. Karacki
Division of Stationary Source
Enforcement
401 M Street, S.W.
Room 3202 WSM (EG-341)
Washington, D.C. 20460
1 Main Files
1 MJKlein
1 PCaputo
1 LLHuff
1 JDStockham
1 Chemical Engineering File
IIT RESEARCH INSTITUTE
55 HTRI-C6333C04-3
------- |